3 1/2 days without a cigarette...

and I am fighting the biggest craving ever! Why is it that I can go three full days with only the slightest passing urge to light up, and now want a cigarette so badly that I'm tempted to get dressed and go to the store and buy a pack? I'm wearing my nicotine patch, and it's not a craving for nicotine, as much as it's a craving for the physical act of lighting up and inhaling. Why now???